Euv light source apparatus

ABSTRACT

A target supply apparatus includes a tank for storing a liquid target material, a nozzle for outputting the liquid target material in the tank, and a gas supply source for supplying gas into the tank, and controls a gas pressure inside the tank with a pressure of the gas supplied from the gas supply source which is provided with a pressure regulator. The target supply apparatus also includes a pressure-decrease gas passage of which one end is connected to the tank and the other end forms an exhaust port, a pressure-decrease valve provided on the pressure-decrease gas passage, and a controller for controlling open/close of the pressure-decrease valve. The controller, when the target material is caused not to output from the nozzle, opens the pressure-decrease valve and decreases the pressure inside the tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 14/047,895,filed on Oct. 7, 2013, which is a Divisional application of applicationSer. No. 12/646,025, filed on Dec. 23, 2009, which is an applicationbased upon and claims the benefit of priority from the prior JapanesePatent Applications No. 2008-328274, filed on Dec. 24, 2008 and No.2009-288898, filed on Dec. 21, 2009; the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a target supply apparatus using for anextreme ultraviolet light source apparatus which generates an extremeultraviolet (EUV) light from a plasma generated by irradiating a targetwith a laser light.

2. Description of the Related Art

In recent years, along with a progress in miniaturization ofsemiconductor device, miniaturization of transcription pattern used inphotolithography in a semiconductor process has developed rapidly. Inthe next generation, microfabrication to the extent of 65 nm to 32 nm,or even to the extent of 30 nm and beyond will be required. Therefore,in order to comply with the demand of microfabrication to the extent of30 nm and beyond, development of such exposure apparatus combining anextreme ultraviolet (EUV) light source for a wavelength of about 13 nmand a reduced reflective optics is expected.

As the EUV light source, there are three possible types, which are alaser produced plasma (LPP) light source using plasma generated byirradiating a target with a laser beam, a discharge produced plasma(DPP) light source using plasma generated by electrical discharge, and asynchrotron radiation (SR) light source using orbital radiant light.Among these light sources, the LPP light source has such advantages thatluminance can be made extremely high as close to the black-bodyradiation because plasma density can be made higher compared with theDPP light source and the SR light source. Moreover, the LPP light sourcealso has an advantage that strong luminescence only with a desiredwavelength band is possible by selecting a target material. Furthermore,the LPP light source has such advantages that there is no constructionsuch as electrode around a light source because the light source is apoint light source with nearly isotropic angular distributions,extremely wide collecting solid angle can be acquired, and so on.Accordingly, the LPP light source having such advantages is expected asa light source for EUV lithography which requires more than severaldozen to several hundred watt power.

In the EUV light source apparatus with the LPP system, firstly, a targetmaterial supplied inside a vacuum chamber is excited by being irradiatedwith a laser light and thus be ionized to become plasma (cf. Japanesepatent application Laid-Open No. 2007-266234). Then, a cocktail lightwith various wavelength components including an EUV light is emittedfrom the generated plasma. Then, the EUV light source apparatus focusesthe EUV light by reflecting the EUV light using an EUV collector minorwhich selectively reflects an EUV light with a desired wavelength, e.g.a 13.5 nm wavelength component. The reflected EUV light is inputted toan exposure apparatus. On a reflective surface of the EUV collectormirror, a multilayer coating with a structure in that thin coating ofmolybdenum (Mo) and thin coating of silicon (Si) are alternatelystacked, for instance, is formed. The multilayer coating has performanceof a high reflectance ratio (of about 60% to 70%) with respect to theEUV light with a 13.5 nm wavelength.

In the conventional target supply apparatus, a target is supplied bypressurizing the inside of the tank in the target supply apparatus withgas from a gas cylinder. However, when there is no need to output theEUV light such as during wafer replacement and adjustment of theexposure apparatus or of the EUV light source apparatus, then the supplyof the target is not needed. Therefore, the supply of the target whenthere is no need to output the EUV light becomes waste of the target.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a target supplyapparatus comprises: a tank for storing a liquid target material; anozzle for outputting the liquid target material in the tank; and a gassupply source for supplying gas into the tank, and the target supplyapparatus controlling a gas pressure inside the tank with a pressure ofthe gas supplied from the gas supply source provided with a pressureregulator, and further comprising: a pressure-decrease gas passage ofwhich one end is connected to the tank and the other end forms anexhaust port; a pressure-decrease valve provided on thepressure-decrease gas passage; and a controller for controllingopen/close of the pressure-decrease valve, wherein the controller, whenthe target material is caused not to output from the nozzle, opens thepressure-decrease valve and decreases the pressure inside the tank.

In accordance with another aspect of the present invention, a controlsystem of a target supply section for controlling a gas pressure insidea tank that stores a liquid target material to be output from a nozzleby the pressure of gas supplied from a gas supply source provided with apressure regulator, the control system comprising: a pressure-increasesystem for increasing the pressure inside the tank to a predeterminedpressure at which the target material is output from the nozzle; apressure-decrease system for decreasing the pressure inside the tank;and a controller, when the target material is to be output from thenozzle, for controlling the pressure-increase system to thereby increasethe pressure inside the tank to the predetermined pressure andmaintaining the pressure, and, when there is not to be output the targetmaterial, for controlling the pressure-decrease system and decreasingthe pressure inside the tank, to thereby stop the output of the targetmaterial or reduce the output of the target material.

In accordance with another aspect of the present invention, a controlsystem of a target supply section for controlling a gas pressure insidea tank that stores a liquid target material to be output from a nozzleby the pressure of gas supplied from a gas supply source provided with apressure regulator, the control system comprising: a pressure-increasegas passage that connects between the gas supply source and the tank andis provided with the pressure regulator; and a pressure-increase valveprovided on the pressure-increase gas passage between the pressureregulator and the tank; a pressure-decrease gas passage that isconnected at one end thereof to the pressure-increase gas passagebetween the tank and the pressure-increase valve and has an exhaust portformed at the other end thereof; a pressure-decrease valve provided onthe pressure-decrease gas passage; a first gas passage connected to thepressure-decrease gas passage on the side of the tank from thepressure-decrease valve; a vacuum pump connected to the other end of thefirst gas passage; a first valve provided on the first gas passage; apressure gauge for detecting pressure inside the passages among thepressure-increase valve, the pressure-decrease valve, and the tank; anda controller, when the target material is to be output from the nozzle,based on the pressure detected by the pressure gauge, for opening thepressure-increase valve and closing the pressure-decrease valve and thefirst valve, to thereby increase the pressure inside the tank, and, whenoutput of the target material from the nozzle is to be stopped, foropening the pressure-decrease valve with the first valve closed, tothereby decrease the pressure inside the tank, and then, for closing thepressure-decrease valve and opening the first valve, to thereby furtherdecrease the pressure inside the tank.

In accordance with another aspect of the present invention, a controlapparatus of a target supply section provided with a control circuit,the control apparatus comprising: a pressure-increase gas passageconnecting between a gas supply source provided with a pressureregulator and the target supply section that outputs a target materialin a tank provided with a nozzle from the nozzle by a pressure of gassupplied from the gas supply source; a pressure-increase valve providedon the pressure-increase gas passage between the pressure regulator andthe tank; a pressure-decrease gas passage of which one end is connectedto the pressure-increase gas passage between the tank and thepressure-increase valve and the other end forms an exhaust port; apressure-decrease valve provided on the pressure-decrease gas passage; afirst gas passage connected to the pressure-decrease gas passage on theside of the tank from the pressure-decrease valve; a vacuum pumpconnected to the other end of the first gas passage; a first valveprovided on the first gas passage; and a pressure gauge for detectingpressure inside the passages among the pressure-increase valve, thepressure-decrease valve, and the tank; and a controller, when the targetmaterial is to be output from the nozzle, based on the pressure detectedby the pressure gauge, for opening the pressure-increase valve andclosing the pressure-decrease valve and the first valve, to therebyincrease the pressure inside the tank, and, when output of the targetmaterial from the nozzle is to be stopped, for opening thepressure-decrease valve with the first valve closed, to thereby decreasethe pressure inside the tank, and then, for closing thepressure-decrease valve and opening the first valve, to thereby furtherdecrease the pressure inside the tank.

In accordance with another aspect of the present invention, a controlcircuit of a target supply section, the control circuit comprising: apressure-increase gas passage that connects between a gas supply sourceprovided with a pressure regulator and the target supply section thatoutputs a target material in a tank provided with a nozzle from thenozzle by a pressure of gas supplied from the gas supply source; apressure-increase valve provided on the pressure-increase gas passagebetween the pressure regulator and the tank; a pressure-decrease gaspassage of which one end is connected to the pressure-increase gaspassage between the tank and the pressure-increase valve and the otherend forms an exhaust port; a pressure-decrease valve provided on thepressure-decrease gas passage; a first gas passage connected to thepressure-decrease gas passage on the side of the tank from thepressure-decrease valve; a vacuum pump connected to the other end of thefirst gas passage; a first valve provided on the first gas passage; anda pressure gauge for detecting pressure inside the passages among thepressure-increase valve, the pressure-decrease valve, and the tank,wherein based on the pressure detected by the pressure gauge, when thetarget material is to be output from the nozzle, the pressure-increasevalve is opened and the pressure-decrease valve and the first valve areclosed, to thereby increase the pressure inside the tank, and whenoutput of the target material from the nozzle is to be stopped, thepressure-decrease valve is opened with the first valve closed, tothereby decrease the pressure inside the tank, and then, thepressure-decrease valve is closed and the first valve is opened, tothereby further decrease the pressure inside the tank.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a configuration of an extremeultraviolet light source apparatus using a target supply apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a detailed configuration of the targetsupply apparatus shown in FIG. 1;

FIG. 3 is an overall flowchart of a pressure switching procedureperformed by a controller shown in FIG. 2;

FIG. 4 is a detailed flowchart of a procedure of a pressure-decreaseprocess shown in FIG. 3;

FIG. 5 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a second embodiment of the presentinvention;

FIG. 6 is an overall flowchart of a pressure switching procedureperformed by a controller shown in FIG. 5;

FIG. 7 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a third embodiment of the presentinvention;

FIG. 8 is an overall flowchart of a pressure switching procedureperformed by a controller shown in FIG. 7;

FIG. 9 is a detailed flowchart of a procedure of a post-pressuredecrease process shown in FIG. 8;

FIG. 10 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a fourth embodiment of the presentinvention;

FIG. 11 is an overall flowchart of a pressure switching procedureperformed by a controller shown in FIG. 10;

FIG. 12 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a fifth embodiment of the presentinvention;

FIG. 13 is a detailed flowchart of a procedure of a pressure-decreaseprocess shown in FIG. 12;

FIG. 14 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a first modification of the fifthembodiment of the present invention;

FIG. 15 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a second modification of the fifthembodiment of the present invention;

FIG. 16 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a third modification of the fifthembodiment of the present invention;

FIG. 17 is a schematic diagram of a detailed configuration of a targetsupply apparatus according to a sixth embodiment of the presentinvention; and

FIG. 18 is an overall flowchart of a pressure switching procedureperformed by a controller shown in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of a target supply apparatus, and a controlsystem, a control apparatus, and a control circuit for the sameaccording to the present invention will be explained below withreference to accompanying drawings.

First Embodiment

FIG. 1 is a schematic diagram of a configuration of an extremeultraviolet light source apparatus using a target supply apparatusaccording to a first embodiment of the present invention. FIG. 2 is aschematic diagram of a detailed configuration of the target supplyapparatus shown in FIG. 1. It should be noted that the extremeultraviolet light source apparatus shown in FIG. 1 adopts a laserproduced plasma (LPP) system for generating an extreme ultraviolet lightby irradiating a target material with a laser beam to excite the targetmaterial.

As shown in FIG. 1, the extreme ultraviolet light source apparatusincludes a vacuum chamber 10 in which an extreme ultraviolet light isgenerated, a target supply section 11 which supplies a target 13 to apredetermined position in the vacuum chamber 10, a gas cylinder 40 whichsupplies gas to pressurize the target 13 in order to supply the target13, a pressure regulator 41 which regulates the pressure of the gas forpressurization, a pressure switch system 25 which switches betweenpressures of the gas for pressurization, a driver laser 15 whichgenerates an excitation laser beam 20 irradiated to the target 13, alaser focusing optics 16 for focusing the excitation laser beam 20generated by the driver laser 15, a collector mirror 14 reflecting so asto collect an extreme ultraviolet light 19 emitted from a plasma 18generated by irradiating the target 13 with the excitation laser beam20, an exhaust system 17 for keeping vacuum inside the vacuum chamber10, and a main controller C which controls the whole extreme ultravioletlight source apparatus.

Here, the target supply section 11, the gas cylinder 40, the pressureregulator 41, and the pressure switch system 25 constitute a targetsupply apparatus 1. Furthermore, the pressure switch system 25 includesa controller 60 which provides at least control for increasing a gaspressure inside the target supply section 11 to a predetermined pressureand maintaining the pressure, a pressure-increase system 25 a whichincreases the gas pressure inside the target supply section 11 andmaintains the gas pressure at a predetermined pressure, and apressure-decrease system 25 b which decreases the gas pressure insidethe target supply section 11. Moreover, the main controller C providesat least a control instruction such as a pressure-increase instructionand a pressure-decrease instruction to the target supply apparatus 1.The case of providing the pressure-increase instruction is a case wherethe exposure apparatus (not shown) using an extreme ultraviolet lightrequires the extreme ultraviolet light, and the case of providing thepressure-decrease instruction is a case where the exposure apparatusdoes not require the extreme ultraviolet light.

Here, the target supply apparatus 1 that supplies the target into thevacuum chamber is provided with a tank 30 filled with a target materialsuch as a molten liquid of Sn, Li, or the like. The target material(molten Sn 34) inside the tank 30 is molten by a heater 33 provided onthe outer wall of the tank 30. The target supply apparatus 1 pressurizesthe tank 30 storing the molten target material with the gas from the gascylinder 40 of which pressure is regulated by the pressure regulator 41.This allows ejection of molten metal (Sn, Li, etc.) as the target 13from a nozzle 31 attached to a front end of the tank 30. The target 13is ejected in the form of jet or droplets. The droplets can be generatedby a continuous jet method, for example. In the continuous jet method,an vibrator such as a piezoelectric element 32 is used to induceperiodic vibrations on the jet surface of the molten metal. This allowsthe droplets with uniform volume to be ejected from the nozzle.

The target 13 is supplied from the target supply apparatus 1 to thepredetermined position in the vacuum chamber 10, and the excitationlaser beam 20 outputted from the driver laser 15 is focused to thepredetermined position in the vacuum chamber 10 through the laserfocusing optics 16. At this time, by irradiating the target 13 with theexcitation laser beam 20, the plasma 18 is generated. Thereafter, theextreme ultraviolet light 19 is emitted from the plasma 18. Thecollector mirror 14 collects the extreme ultraviolet light 19 andoutputs the light to the exposure apparatus side (not shown) connectedto the vacuum chamber 10. If the excitation laser beam 20 is a pulsedlaser beam, an irradiation timing of the target 13 and a pulsegeneration timing are synchronously controlled by the main controller C.

In the extreme ultraviolet light source apparatus, for example, metal(liquid or solid Sn, Li) is used as the target 13, and carbon dioxide(CO₂) laser capable of generating a light with a relatively longwavelength is used as the driver laser 15. One of metals with a highconversion efficiency from laser light energy to extreme ultravioletlight energy is Sn. The conversion efficiency when the carbon dioxidelaser is irradiated to the Sn is about 2% to 4%.

The laser focusing optics 16 is composed of at least one lens and/or atleast one minor. As shown in FIG. 1, the laser collecting optics 16 maybe provided outside the vacuum chamber 10 or may be provided inside thevacuum chamber 10.

The collector mirror 14 is a collecting optics that selectively reflectsa predetermined wavelength component (e.g., extreme ultraviolet light ofnear 13.5 nm) from among various wavelength components emitted from theplasma 18 and collects the component. The collector mirror 14 has aconcave reflecting surface. On the reflecting surface, a multilayercoating of molybdenum (Mo) and silicon (Si) which selectively reflectthe extreme ultraviolet light with wavelength near 13.5 nm is formed.

As shown in FIG. 2, the target supply section 11 includes the tank 30that stores the molten Sn 34 inside thereof and has the capability tomaintain the internal pressure at, for example, a high pressure or at apredetermined pressure, the heater 33 provided on the outer side of thetank 30 and provided as a heat regulator for melting Sn in the tank 30,the nozzle 31 for ejecting the molten Sn as the target 13, and thepiezoelectric element 32 that is provided near the nozzle 31 and causesthe target 13 to be continuously ejected as droplets from the nozzle 31.

The pressure regulator 41 autonomously performs pressure regulation sothat the gas supplied from the gas cylinder 40 becomes a setpredetermined gas pressure. The pressure regulator 41 and the tank 30are connected to each other by gas passages L1 and L. On the gas passageL1, a valve 42 for opening and closing the passage is provided.Meanwhile, a gas passage L2 is branched from a connection point P1between the gas passages L1 and L. An exhaust port La is formed at theother end of the gas passage L2. On the gas passage L2, a valve 43 foropening and closing the passage is provided. Furthermore, a gas passageL3 is branched from a connection point P2 between the valve 43 and theconnection point P1. A vacuum pump 46 is connected to the other end ofthe gas passage L3. Moreover, a valve 44 for opening and closing thepassage is provided on the gas passage L3 between the vacuum pump 46 andthe connection point P2. Near the connection point P1, a pressure gauge45 for detecting a pressure inside the gas passages is provided. Thecontroller 60 controls the open/close of the valves 42, 43, and 44 andcontrols the drive of the vacuum pump 46 based on an instruction fromthe main controller C and a pressure value of the pressure gauge 45.

Here, a pressure switching control procedure in the tank 30 performed bythe controller 60 is explained with reference to the flowcharts shown inFIG. 3 and FIG. 4. As shown in FIG. 3, first, the controller 60 closesthe valves 42, 43, and 44 as an initial setting (Step S101), and then,sets the pressure used upon supply of the target, as a set pressure ofthe pressure regulator 41 (Step S102). The setting at Step S102 ispreviously manually performed in the first embodiment. Thereafter, thecontroller 60 determines whether an instruction to increase the pressurehas been received from the main controller C (Step S103). If noinstruction to increase the pressure has been received (No at StepS103), the controller 60 repeats the determination process performed atStep S103. Meanwhile, if the instruction to increase the pressure hasbeen received (Yes at Step S103), the controller 60 opens the valve 42(Step S104), to thereby increase the pressure inside the tank 30 throughthe gas passages L1 and L. This allows the pressure inside the tank 30to become a pressure required for supplying the target 13.

Thereafter, the controller 60 determines whether an instruction todecrease the pressure has been received from the main controller C (StepS105). If no instruction to decrease the pressure has been received (Noat Step S105), the controller 60 maintains the open state of the valve42. Thus, the pressure regulation for maintaining a predeterminedpressure state inside the tank 30 by the pressure regulator 41 can beexecuted. Meanwhile, if the instruction to decrease the pressure hasbeen received (Yes at Step S105), the controller 60 closes the valve 42(Step S106), to thereby ends the pressure-increase process, and thenperforms the pressure-decrease process (Step S107). After thepressure-decrease process, the controller 60 further determines whetheran instruction to increase the pressure has been received (Step S108).If the instruction to increase the pressure has been received (Yes atStep S108), the controller 60 moves to Step S104 and opens the valve 42which has been closed during the pressure-decrease process to restartthe pressure-increase process. Meanwhile, if no instruction to increasethe pressure has been received (No at Step S108), the controller 60further determines whether an end instruction has been received from themain controller C (Step S109). If no end instruction has been received(No at Step S109), the controller 60 moves to Step S108, and waits untilan instruction to increase the pressure is received. Meanwhile, if theend instruction has been received (Yes at Step S109), the controller 60ends the present process.

In the pressure-decrease process at Step S107, as shown in FIG. 4,first, the controller 60 starts the vacuum pump 46 (Step S111). Itshould be noted that the vacuum pump 46 may be set to be on normally.The normally-on of the vacuum pump 46 allows reduction of apressure-decrease time. Thereafter, the controller 60 opens the valve 43(Step S112), and thereby exhausts the gas pressurizing inside the tank30 to the exhaust port La. This causes the pressure inside the tank 30to decrease. Here, because the inside of the vacuum chamber 10 suppliedwith the target 13 is vacuum, even if the pressure inside the tank 30becomes about atmospheric pressure, the supply of the target 13 will notbe stopped due to a differential pressure between the pressure insidethe vacuum chamber 10 and the pressure inside the tank 30. To stop thesupply of the target 13, it is necessary to decrease the pressure insidethe pump 30 to a range of tens of Pa to hundreds of Pa. Therefore, thecontroller 60 determines, as a next process, whether a measured value Pof the pressure gauge 45 has become equal to or below a pressure Phigh(e.g., a pressure of 1.1 atmospheres) which is slightly above theatmospheric pressure (Step S113).

If the measured value P of the pressure gauge 45 is not equal to orbelow the pressure Phigh (No at Step S113), the controller 60 repeatsthe determination process performed at Step S113. Meanwhile, if themeasured value P of the pressure gauge 45 is equal to or below thepressure Phigh (Yes at Step S113), the controller 60 closes the valve 43(Step S114), and further opens the valve 44 (Step S115). This causes thevacuum pump 46 to exhaust the gas from the tank 30, and the inside ofthe tank 30 is thereby evacuated.

Thereafter, the controller 60 further determines whether the measuredvalue P of the pressure gauge 45 has become equal to or below thepressure Plow (e.g., a range of tens of Pa to hundreds of Pa) at whichthe supply of the target 13 is stopped (Step S116). If the measuredvalue P of the pressure gauge 45 is not equal to or below the pressurePlow (No at Step S116), the controller 60 repeats the determinationprocess performed at Step S116. Meanwhile, if the measured value P ofthe pressure gauge 45 is equal to or below the pressure Plow (Yes atStep S116), then the controller 60 closes the valve 44 (Step S117). Itshould be noted that the pressure Plow at which the supply of the targetis stopped is dependent on the diameter of the nozzle 31, and aremaining amount and a temperature of the target 13. Thereafter, if thevacuum pump 46 is not on normally, the controller 60 stops the vacuumpump 46 (Step S118), and returns to Step S107. It is noted that if thevacuum pump 46 is on normally, the controller 60 does not execute theprocess at Step S117, and returns to Step S107 as it is.

As explained above, the first embodiment is configured so as to supplyand stop the target 13 by disposing the pressure switch system 25between the pressure regulator 41 and the tank 30 of the target supplysection 11 and performing the pressure-increase process and thepressure-decrease process inside the tank 30 using the pressure switchsystem 25. This configuration allows the supply of the target 13 to bestopped when output of the EUV light is not required in the firstembodiment. As a result of this, wasteful consumption of the target issuppressed, which allows achievement of the extreme ultraviolet lightsource apparatus in which the consumption of the target 13 issuppressed.

Second Embodiment

Next, a second embodiment of the present invention will be explainedbelow. FIG. 5 is a schematic diagram of a detailed configuration of atarget supply apparatus according to the second embodiment of thepresent invention. As shown in FIG. 5, in a target supply apparatus 2according to the second embodiment, a gas passage L4 is connected to aconnection point P3 between the pressure regulator 41 and the valve 42of the target supply apparatus 1 according to the first embodiment. Atank 47 is provided at the other end of the gas passage L4. On the gaspassage L4, a valve 48 is provided. The capacity of the tank 47 is largeas compared with the capacity of the tank 30, which is, for example,about 10 times as large as that of the tank 30. The rest of theconfiguration is the same as the configuration of the target supplyapparatus 1 shown in FIG. 2, and thus, the same numerals are assigned tothe same components.

A pressure-increase time required for increasing the pressure inside thetank 30 is determined by a gas flow rate at which gas can be flowedthrough the pressure regulator 41. Therefore, if the gas flow rate islow, the pressure-increase time becomes longer. Therefore, in the secondembodiment, pressure gas previously filled in the tank 47 for increasingthe pressure is used to compensate the gas flow rate. This allowsreduction of the pressure-increase time requiring for increasing thepressure inside the tank 30.

Here, a pressure switching control procedure in the tank 30 performed bya controller 61 corresponding to the controller 60 is explained withreference to the flowchart shown in FIG. 6. As shown in FIG. 6, first,the controller 61 closes the valves 42, 43, 44, and 48 as an initialsetting (Step S201), and then, sets the pressure used upon supply of thetarget, as a set pressure of the pressure regulator 41 (Step S202).Thereafter, the controller 61 opens the valve 48 (Step S203) anddetermines whether an instruction to increase the pressure has beenreceived from the main controller C (Step S204). If no instruction toincrease the pressure has been received (No at Step S204), thecontroller 61 repeats the determination process performed at Step S204.Meanwhile, if the instruction to increase the pressure has been received(Yes at Step S204), the controller 61 opens the valve 42 (Step S205), tothereby obtain an assist pressure of the tank 47 and increase thepressure inside the tank 30 through the gas passages L4, L1, and L. Thiscauses the pressure inside the tank 30 to be a pressure required forsupplying the target 13. Thereafter, the controller 61 closes the valve48 after a set time passes and further after, for example, severalseconds pass (Step S206). This is because there may be a case where thepressure inside the tank 30 does not reach a pressure to be used only byintroducing the gas in the tank 47 into the tank 30. Therefore, bysupplying the gas from the gas cylinder 40 thereto several secondslonger than the set time through the pressure regulator 41, the gas flowrate supplied to the tank 30 is increased. The reason why the valve 48is closed at Step S206 is because a piping capacity of the gas passageconnected to the tank 30 is reduced. By closing the gas passage not usedby the valve, the supply time of gas can be reduced. It is noted thatthe process at Step S206 may be omitted.

Thereafter, similarly to the first embodiment, the controller 61determines whether an instruction to decrease the pressure has beenreceived from the main controller C (Step S207). If no instruction todecrease the pressure has been received (No at Step S207), thecontroller 61 maintains the open state of the valve 42. This causes thepressure regulator 41 that maintains a predetermined pressure state inthe tank 30 to perform the pressure regulation. Meanwhile, if theinstruction to decrease the pressure has been received (Yes at StepS207), the controller 61 closes the valve 42 (Step S208), to thereby endthe pressure-increase process, and then performs a pressure-decreaseprocess (Step S209). The pressure-decrease process is the process shownin FIG. 4. After the pressure-decrease process, the controller 61further opens the valve 48 (Step S210), to thereby set the pressureinside the tank 47 to a predetermined pressure state.

Thereafter, the controller 61 further determines whether an instructionto increase the pressure has been received (Step S211). If theinstruction to increase the pressure has been received (Yes at StepS211), the controller 61 moves to Step S205 and opens the valve 42 whichhas been closed during the pressure-decrease process, to restart thepressure-increase process using the tank 47. Meanwhile, if noinstruction to increase the pressure has been received (No at StepS211), the controller 61 further determines whether an end instructionhas been received from the main controller C (Step S212). If no endinstruction has been received (No at Step S212), the controller 61 movesto Step S211, and waits until an instruction to increase the pressure isreceived. Meanwhile, if the end instruction has been received (Yes atStep S212), the controller 61 ends the present process.

As explained above, in the second embodiment, similarly to the firstembodiment, it is possible to supply and stop the target material asrequired. Therefore, if there is no need to output the EUV light, thesupply of the target 13 can be stopped. As a result of this, wastefulconsumption of the target is suppressed, which allows achievement of theextreme ultraviolet light source apparatus with less consumption of thetarget 13. Particularly, in the second embodiment, the tank 47 assistsin increasing the pressure upon increase of the pressure, and thus, thepressure-increase time can be reduced. Consequently, it is possible toachieve the extreme ultraviolet light source apparatus in which theconsumption of the target 13 is further suppressed.

Third Embodiment

Next, a third embodiment of the present invention will be explainedbelow. FIG. 7 is a schematic diagram of a configuration of a targetsupply apparatus according to the third embodiment of the presentinvention. As shown in FIG. 7, in a target supply apparatus 3 accordingto the third embodiment, a tank 49 is provided in place of the exhaustport La of the gas passage L2 shown in the first embodiment. The tank 49has a large capacity as compared with the capacity of the tank 30, whichis, for example, about 100 times as large as that of the tank 30. In thetank 49, a gas passage L5 connected to a connection point P3 on the gaspassage L3 between the valve 44 and the vacuum pump 46 is furtherprovided. On the gas passage L5, a valve 50 is provided. A pressuregauge 51 that detects the pressure inside the tank is provided in thetank 49. The rest of the configuration is the same as the configurationof the target supply apparatus 1 shown in FIG. 2, and thus, the samenumerals are assigned to the same components.

For example, if an exhaust line from the tank 30 to the exhaust port Lais long and a passage resistance is high, a long time is required todecrease the pressure inside the tank 30 to about atmospheric pressure.Therefore, in the third embodiment, by connecting the tank 49 with largecapacity in which the pressure is decreased to the pressure belowatmospheric pressure to the exhaust line, a pressure gradient of theexhaust line is increased. As a result, an exhaust flow rate of theexhaust line increases, which allows an exhaust time to be reduced.

Here, a pressure switching control procedure in the tank 30 performed bya controller 62 corresponding to the controller 60 is explained withreference to the flowcharts shown in FIG. 8 and FIG. 9. FIG. 8 is anoverall flowchart of the pressure switching control procedure performedby the controller 62. As is clear from comparison between FIG. 8 andFIG. 3, in the third embodiment, a post-pressure decrease process afterthe pressure-decrease process is performed (Step S308) is executedbetween Step S107 and Step S108 shown in FIG. 3. The other processes arethe same as these of the first embodiment. It should be noted that StepS301 to Step S307 in FIG. 8 correspond to Step S101 to Step S107 in FIG.3, and Step S309 and Step S310 in FIG. 8 correspond to Step S108 to StepS109 in FIG. 3.

FIG. 9 is a detailed flowchart of a procedure of a post-pressuredecrease process performed at Step S308 in FIG. 8. The post-pressuredecrease process is a process, as a preparation process for a nextpressure-decrease process, for evacuating the inside the tank 49 todecrease the pressure. In FIG. 9, first, the controller 62 starts thevacuum pump 46 (Step S401). It should be noted that the vacuum pump 46may be set to be on normally. The normally-on of the vacuum pump 46allows reduction of a pressure-decrease time. Thereafter, the controller62 opens the valve 50 (Step S402), and thereby exhausts the gas from thetank 49.

Thereafter, the controller 62 determines whether a measured value P ofthe pressure gauge 51 is equal to or below a vacuum pressure Pv, forexample, equal to or below 1 Pa (Step S403). If the measured value P ofthe pressure gauge 51 is not equal to or below the vacuum pressure Pv(No at Step S403), the controller 62 repeats the determination processperformed at Step S403. Meanwhile, if the measured value P of thepressure gauge 51 is equal to or below the vacuum pressure Pv (Yes atStep S403), the controller 62 closes the valve 50 (Step S404), furtherstops the vacuum pump 46 (Step S405), and, then, returns to Step S308.When the vacuum pump 46 is on normally, the controller 62 returns toStep S308 as it is after the process at step S404.

As explained above, in the third embodiment, similarly to the firstembodiment, it is possible to supply and stop the target material asrequired. Therefore, when there is no need to output the EUV light, thesupply of the target 13 can be stopped. As a result of this, wastefulconsumption of the target is suppressed, which allows achievement of theextreme ultraviolet light source apparatus with less consumption of thetarget 13. Particularly, in the third embodiment, the tank 49 is used toperform the pressure-decrease process, and thus, the pressure gradientof the exhaust line from the tank 30 can be increased. Consequently, itis possible to increase the exhaust flow rate, which allows furtherreduction of the pressure-decrease time.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be explainedbelow. FIG. 10 is a schematic diagram of a configuration of a targetsupply apparatus according to the fourth embodiment of the presentinvention. As shown in FIG. 10, in a target supply apparatus 4 accordingto the fourth embodiment, a pressure controller 52 is provided on thegas passage L1 between the pressure regulator 41 and the valve 42 of thetarget supply apparatus 1 according to the first embodiment, and a gaspassage L6 connecting between connection points P5 and P6 on the gaspassage L1 on an input side and an output side of the pressurecontroller 52 is provided to bypass the pressure controller 52. Further,a valve 53 is provided on the gas passage L1 between the connectionpoint P5 and the pressure controller 52, and a valve 54 is provided onthe gas passage L6. The rest of the configuration is the same as theconfiguration of the target supply apparatus 1 shown in FIG. 2, andthus, the same numerals are assigned to the same components.

Here, the pressure to pressurize the molten Sn 34 being the targetmaterial in the tank 30 affects the velocity of the target 13.Therefore, it is preferable to keep constant the pressure inside thetank 30. Generally, the pressure is regulated by the pressure regulator41. It is noted that pressure control with higher precision may berequested dependent on purposes. Therefore, in the fourth embodiment,the pressure controller 52 for performing pressure control with highprecision is provided on the gas passage L1. It is noted that a maximumgas flow rate of the high-precision pressure controller 51 is low.Because of this, when the pressure is to be increased through thepressure controller 51, it takes a long time until the pressure reachesa desired pressure. Therefore, in the fourth embodiment, there isprovided the gas passage L6 as a bypass line for bypassing the gaspassage L1, and when high-precision pressure control is performed by thepressure controller 52, the gas is flowed through the gas passage L6.This allows reduction of the pressure-increase time even if the pressurecontroller 52 is provided on the gas passage L1.

Here, a pressure switching control procedure in the tank 30 performed bya controller 63 corresponding to the controller 60 is explained withreference to the flowchart shown in FIG. 11. As shown in FIG. 11, first,the controller 63 closes the valves 42, 43, 44, 53, and 54, as initialsetting (Step S501). Then, the controller 63 sets a pressure higher thanthe pressure used upon supply of the target, for example, a pressure of1.1 times as high as the pressure used, as a set pressure of thepressure regulator 41 (Step S502). The set pressure may be preset or maybe set by the controller 63. Thereafter, the controller 63 determineswhether an instruction to increase the pressure has been received fromthe main controller C (Step S503). If no instruction to increase thepressure has been received from the main controller C (No at Step S503),the controller 63 repeats the determination process performed at StepS503. Meanwhile, if the instruction to increase the pressure has beenreceived from the main controller C (Yes at Step S503), the controller63 opens the valves 54 and 42 (Step S504), to thereby increase thepressure inside the tank 30.

Thereafter, the controller 63 determines whether a measured value P ofthe pressure gauge 45 has become equal to or higher than 90% of aworking pressure used upon supply of the target (Step S505). If themeasured value P of the pressure gauge 45 is not equal to or higher than90% of the working pressure (No at Step S505), the controller 63 repeatsthe determination process performed at Step S505 and continues thepressure-increase process. Meanwhile, if the measured value P of thepressure gauge 45 is equal to or higher than 90% of the working pressure(Yes at Step S505), the controller 63 closes the valve 54 (Step S506),and further opens the valve 53 and uses the pressure controller 52 toincrease the pressure inside the tank 30 to the working pressure usedfor supplying the target (Step S507).

Thereafter, the controller 63 determines whether an instruction todecrease the pressure has been received from the main controller C (StepS508). If no instruction to decrease the pressure has been received fromthe main controller C (No at Step S508), the controller 63 repeats thedetermination process performed at Step S508, and thereby causes thepressure controller 52 to perform pressure control with high precision.Meanwhile, if the instruction to decrease the pressure has been receivedfrom the main controller C (Yes at Step S508), the controller 63 closesthe valves 42 and 53, and thereby stops the pressure control by thepressure controller 52 (Step S509). Thereafter, the controller 63performs the pressure-decrease process the same as that at Step S107(Step S510).

After the pressure-decrease process at Step S510, the controller 63further determines whether an instruction to increase the pressure hasbeen received (Step S511). If the instruction to increase the pressurehas been received (Yes at Step S511), the controller 63 moves to StepS504 and restarts the pressure-increase process. Meanwhile, if noinstruction to increase the pressure has been received (No at StepS511), the controller 63 further determines whether an end instructionhas been received from the main controller C (Step S512). If no endinstruction has been received (No at Step S512), the controller 63 movesto Step S511, and waits until an instruction to increase the pressure isreceived. Meanwhile, if the end instruction has been received (Yes atStep S512), the controller 63 ends the present process.

As described above, in the fourth embodiment, similarly to the firstembodiment, it is possible to supply and stop the target material asrequired. Therefore, if there is no need to output the EUV light, thesupply of the target 13 can be stopped. As a result of this, wastefulconsumption of the target is suppressed, which allows achievement of theextreme ultraviolet light source apparatus with less consumption of thetarget 13. Particularly, in the fourth embodiment, there is provided thegas passage L6 as the bypass line for bypassing the gas passage L1, andwhen high-precision pressure control is performed by the pressurecontroller 52, the gas is introduced through the gas passage L6.Therefore, the pressure inside the tank 30 can be increased in a shorttime even if the high-precision pressure controller 52 is provided onthe gas passage L1.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be explainedbelow. FIG. 12 is a schematic diagram of a configuration of a targetsupply apparatus according to the fifth embodiment of the presentinvention. As shown in FIG. 12, a target supply apparatus 5 according tothe fifth embodiment has the same configuration as that of the targetsupply apparatus 1 according to the first embodiment. It is noted that,in the target supply apparatus 5 according to the fifth embodiment, thevacuum pump 46, the gas passage L3, and the valve 44 in the targetsupply apparatus 1 are deleted. The rest of the configuration is thesame as the configuration of the target supply apparatus 1 shown in FIG.2, and thus, the same numerals are assigned to the same components.

Here, in the first embodiment, when the supply of the target 13 is to bestopped, the inside of the tank 30 is evacuated by the vacuum pump to arange of tens of Pa to hundreds of Pa, and thus it takes a long time tostop the supply. Meanwhile, if the evacuation is up to about theatmospheric pressure, the evacuation by the vacuum pump is not needed,and thus, an evacuation time can be reduced. Here, a velocity V uponsupply of the target material can be expressed by the following Equation(1).

$\begin{matrix}{V = \sqrt{2 \times \frac{{\Delta \; P} - {Ph}}{\rho}}} & (1)\end{matrix}$

In the Equation (1), ΔP is a pressure for pressurizing the targetmaterial, Ph is a pressure loss, and ρ is a density of the targetmaterial.

It is understood from the Equation (1) that when the pressurizationpressure is decreased from several MPa to atmospheric pressure (0.1MPa), the velocity of the target material becomes about one-tenth.Accordingly, by decreasing the pressure for pressurizing the targetmaterial to about atmospheric pressure, the amount of consumption of thetarget material can be largely reduced. Therefore, in the fifthembodiment, by decreasing the pressure inside the tank 30 to aboutatmospheric pressure, the amount of consumption of the target 13 can belargely reduced. This allows achievement of the extreme ultravioletlight source apparatus capable of largely suppressing the amount ofconsumption of the target material when the EUV light is not required.In addition, the configuration of decreasing the pressure inside thetank 30 to about atmospheric pressure can be implemented with a simpleconfiguration, and thus, the configuration of the extreme ultravioletlight source apparatus can be also simplified.

Here, a procedure of a pressure-decrease process performed by acontroller 64 corresponding to the controller 60 will be explained belowwith reference to the flowchart shown in FIG. 13. It should be notedthat the pressure-increase process is the same as that of the firstembodiment. However, the procedure of the pressure-decrease process isdifferent from that performed at Step S107 shown in FIG. 3. As shown inFIG. 13, first, the controller 64 opens the valve 43 (Step S601), tothereby exhaust the gas pressurizing the inside of the tank 30 to aboutatmospheric pressure. Thereafter, the controller 64 determines whether ameasured value P of the pressure gauge 45 has become equal to or below apressure Phigh which is slightly above the atmospheric pressure, forexample, equal to or below a pressure of 1.1 atmospheres (Step S602). Ifthe measured value P of the pressure gauge 45 is not equal to or belowthe pressure Phigh (No at Step S602), the controller 64 repeats thedetermination process performed at Step S602. Meanwhile, if the measuredvalue P of the pressure gauge 45 is equal to or below the pressure Phigh(Yes at Step S602), the controller 64 closes the valve 43 (Step S603),and then returns to Step S107.

As described above, in the fifth embodiment, it is possible to supplythe target material and reduce the amount of supply thereof as required.Therefore, it is possible to reduce the amount of supply of the target13 with a simple configuration. As a result of this, wastefulconsumption of the target material can be suppressed without using acomplicated configuration such as a vacuum pump, and this allowsachievement of the extreme ultraviolet light source apparatus with lessconsumption of the target 13.

It is possible to achieve a target supply apparatus provided with thepressure switch system 25 in which the pressure-increase system and thepressure-decrease system according to the first to the fifth embodimentsare combined as necessary. Moreover, the pressure-decrease system or thelike can be modified as required. One examples of modifications will beexplained below.

First Modification

FIG. 14 is a schematic diagram of a configuration of a target supplyapparatus according to a first modification in which the configurationof the pressure increase side shown in the second embodiment is appliedto the configuration shown in the fifth embodiment. More specifically,the first modification uses the configuration shown in the secondembodiment as the pressure-increase system, and uses the configurationshown in the fifth embodiment as the pressure-decrease system. Thisenables, in the pressure-increase process, the pressure to be increasedby the tank 47 in a short time, similarly to the second embodiment. Thisalso enables, in the pressure-decrease process, the consumption of thetarget material to be suppressed with a simple configuration, similarlyto the fifth embodiment.

Second Modification

FIG. 15 is a schematic diagram of a configuration of a target supplyapparatus according to a second modification in which the configurationof the pressure-decrease system shown in the third embodiment issimplified. As shown in FIG. 15, in the second modification, the gaspassage L3 and the valve 44 shown in the third embodiment are deleted,and the connection point P3 of the gas passage L5 is connected to thevacuum pump 46. The rest of the configuration is the same as that of thethird embodiment. In the second modification, by previously evacuatingthe inside the tank 49 by the vacuum pump 46 before thepressure-decrease process, it is possible to perform thepressure-decrease process with a simple configuration and in a shorttime.

Third Modification

FIG. 16 is a schematic diagram of a configuration of a target supplyapparatus according to a third modification in which the configurationof the pressure increase side shown in the fourth embodiment is appliedto the configuration shown in the fifth embodiment. More specifically,the third modification uses the configuration shown in the fourthembodiment as the pressure-increase system, and uses the configurationshown in the fifth embodiment as the pressure-decrease system. Thisenables, in the pressure-increase process, the pressure to be increasedin a short time and high-precision pressure control to be performed,similarly to the fourth embodiment. This also enables wastefulconsumption of the target material to be suppressed with a simpleconfiguration, similarly to the fifth embodiment.

In the first to the fifth embodiments and the first to the thirdmodifications, the gas passage directly connected to the tank 30 is thecommon gas passage L. However, it is not limited to the configuration.For example, the gas passage L1 on the pressure increase side and thegas passage L2 on the pressure decrease side may be separately connectedto the tank 30.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be explainedbelow. The first to the fifth embodiments and the modifications adoptthe continuous jet method as a target supply method. Therefore, in thefirst to the fifth embodiments and the modifications, the pressureinside the tank 30 is maintained at a comparatively high pressure ofabout several MPa to a dozen MPa or so. On the other hand, the sixthembodiment adopts an electrostatic attraction method. In theelectrostatic attraction method, an electrode is disposed in a positionopposite to a nozzle tip. For example, when the nozzle tip is groundedand a voltage is applied to the electrode, then an electrostaticattractive force is exerted on the target material. The electrostaticattractive force and the gas pressure inside the tank cause the targetmaterial to be ejected from the nozzle tip in the form of droplets. Asexplained above, in the target supply apparatus adopting theelectrostatic attraction method, by applying the voltage to theelectrode, the electrostatic attractive force works. Therefore, thepressure inside the tank that stores the target material may be acomparatively low pressure, for example, a pressure equal to or lessthan 1 MPa, as compared with the case in which the continuous jet methodis adopted.

Here, one example of the target supply apparatus according to the sixthembodiment will be explained. In the following explanation, there isexemplified a case where the electrostatic attraction method is adoptedto the target supply apparatus 1 according to the first embodiment.However, it is not limited thereto, and thus, the sixth embodiment canbe applied to any one of the second to the fifth embodiments and themodifications thereof.

FIG. 17 is a schematic diagram of a configuration of the target supplyapparatus according to the sixth embodiment. As shown in FIG. 17, in atarget supply apparatus 6 according to the sixth embodiment, the targetsupply section 11 is replaced with a target supply section 21 based onthe same configuration as that of the target supply apparatus 1 shown inFIG. 2. The target supply section 21 includes, in addition to the sameconfiguration as that of the target supply section 11, an electrode 36disposed opposite to a nozzle tip 31 a, and an insulation portion 35 forinsulating between the electrode 36 and a nozzle tip 31 a and fixing aspace therebetween to be separated by a certain distance d. At a portionof the electrode 36 corresponding to the nozzle 31 or along a path ofejection of the target 13, a hole 36 a for passing the target 13therethrough is formed.

To the electrode 36, a voltage signal to generate an electric field thatattracts the target material from the nozzle 31 is inputted. The voltagesignal may be a pulse signal such as a square wave, a triangle wave, ora sine (cosine) wave, or may be a constant voltage signal. Moreover, thenozzle tip 31 a may be grounded or may be applied with a potentialhaving a polarity opposite to the polarity of the voltage signal. Byapplying a high-precision voltage signal, the force (electrostaticattractive force) of attracting the target material being molten metalfrom the nozzle 31 can be kept constant. Furthermore, the nozzle tip 31a being a tip portion of the nozzle 31 conically projects toward thedirection of ejection of the target 13. This allows the electric fieldformed between the electrode 36 and the nozzle 31 to be focused on nearthe nozzle tip 31 a. As a result, it is possible to efficiently attractthe target material from the nozzle 31 and eject it as the target 13.

As explained above, even in the target supply apparatus 6 using theso-called electrostatic attraction method for using the electrostaticattractive force to actively eject the target 13 from the nozzle 31 in adrop-on-demand manner, it is preferable to keep the pressure inside thetank 30 to be a constant pressure (<1 MPa), similarly to the first tothe fifth embodiments and the modifications thereof.

It should be noted that the pressure for pressurizing the inside of thetank may be about a critical value at which the target material (moltenSn) is output from the nozzle tip 31 a. A critical value P can beexpressed by the following Equation (3).

$\begin{matrix}{P = {\frac{2\gamma}{r} - {\rho \times {gh}}}} & (2)\end{matrix}$

In the Equation (3), γ is a surface tension of the target material, r isa radius of the hole of the nozzle tip 31 a, ρ is a density of thetarget material, g is an acceleration of gravity, and h is a height fromthe nozzle tip 31 a to an upper surface of liquid level of the targetmaterial.

Here, if the surface tension of the target material be γ=0.573 [N/m],the radius of the hole of the nozzle tip 31 a be r=5 [N/m], the densityof the target material be ρ=7000 [kg/m³], the acceleration of gravity beg=9.8 [N/s], and the height from the nozzle tip 31 a to the uppersurface of liquid level of the target material be h=0.2 [m], then acritical value of the gas pressure becomes P=215 [kPa].

Moreover, it is understood that an allowable fluctuation range of thepressure inside the tank 30 (for example, a value to such an extent thata fluctuation can be regarded as an error) in the case of using theelectrostatic attraction method is about ±10 Pa if the value be equal toor less than 5% of the fluctuation. In this manner, by suppressing afluctuation range of the pressure inside the tank 30 to within a smallfluctuation range of, for example, ±10 Pa or less, a velocityfluctuation of the target 13 is reduced, so that a fluctuation of theposition on which the EUV light is collected can be suppressed. As aresult, it is possible to achieve the extreme ultraviolet light sourceapparatus capable of reducing unevenness of exposure occurring in anexposure device. The sixth embodiment also provides the heater 33 forcontrolling the temperature of the molten Sn 34 to be constant, and thiscauses the velocity fluctuation of the target 13 to be less, so that thefluctuation of the position on which the EUV light is collected can befurther suppressed. Consequently, it is possible to achieve the extremeultraviolet light source apparatus capable of further reducing theunevenness of exposure occurring in an exposure device.

Next, a pressure switching control procedure in the tank 30 performed bya controller 68 corresponding to the controller 60 is explained withreference to the flowchart shown in FIG. 18. FIG. 18 is an overallflowchart of a pressure switching control procedure performed by thecontroller 68. As is clear from comparison between FIG. 18 and FIG. 3,in the sixth embodiment, a process (Step S601) for applying a voltagefor ejection of the target to the electrode 36 is executed between StepS101 and Step S102 shown in FIG. 3, and a process (Step S602) forstopping application of the voltage to the electrode 36 is executedafter Step S109 shown in FIG. 3. The rest of the steps are the same asthese of FIG. 3, and thus, detailed explanation thereof is omitted. Itis noted that as a result of Step S104, the gas pressure inside the tank30 is controlled to a pressure which is about the critical value due tothe Equation (2) and at which the target 13 is output from the nozzle 31with the voltage applied to the electrode 36. Furthermore, thepressure-decrease process at Step S107 is the same as that explainedwith reference to FIG. 4.

Based on the configuration and the operations, even in the target supplyapparatus adopting the electrostatic attraction method as shown in thesixth embodiment, the same effects as these in the embodiments and themodifications can be obtained.

As explained above, according to the embodiments of the presentinvention, if there is no need to eject a molten target material, it ispossible to decrease the pressure inside the tank by using the valve forpressure decrease provided on the gas passage for pressure decrease.Therefore, it is possible to achieve the target supply apparatus, thecontrol system, the control apparatus, and the control circuit capableof reducing waste of the target.

It should be noted that the embodiments and the modifications are onlyexamples of implementing the present invention, and thus, the presentinvention is not limited thereto. Therefore, it is apparent from thedescription that various modifications according to specifications orthe like fall within the scope of the present invention, andfurthermore, that other various embodiments are possible within thescope of the present invention. Moreover, the embodiments and themodifications can be mutually combined as required.

1. An extreme ultraviolet light source apparatus comprising: a targetsupply apparatus including: a tank for storing a liquid target material;a nozzle for outputting the liquid target material in the tank; and agas supply source for supplying gas into the tank, and the target supplyapparatus controlling a gas pressure inside the tank with a pressure ofthe gas supplied from the gas supply source provided with a pressureregulator; a chamber in which an extreme ultraviolet light is generated,by irradiating the liquid target material outputted from the nozzle witha laser beam; a collector mirror provided in the chamber and configuredto collect the generated extreme ultraviolet light; a first gas passageconnected to the tank, the gas from the tank being exhausted through thefirst gas passage; a first valve provided on the first gas passage; asecond gas passage connected to the first gas passage between the tankand the first valve; a second valve provided on the second gas passage;and a controller configured to control open/close of the first valve andthe second value, wherein the controller closes the first valve andopens the second valve such that the gas from the tank flowing throughthe first gas passage is exhausted through the second gas passage. 2.The extreme ultraviolet light source apparatus according to claim 1,further comprising a gas supply passage provided separately from thefirst gas passage and the second gas passage, and configured to connectbetween the gas supply source and the tank.
 3. The extreme ultravioletlight source apparatus according to claim 1, wherein, in order todecrease a gas pressure inside the tank when the liquid target materialis outputted from the nozzle, the controller controls the open/close ofthe first valve and the second valve such that: the controller opens thefirst valve and closes the second valve to exhaust the gas from the tankthrough the first gas passage, until the gas pressure inside the firstgas passage reaches a predetermined gas pressure; and the controllercloses the first valve and opens the second valve to exhaust the gasfrom the tank through the second gas passage, after the gas pressureinside the first gas passage reaches the predetermined gas pressure. 4.The extreme ultraviolet light source apparatus according to claim 3,wherein: a range of the gas pressure inside the first gas passage fromwhen the liquid target material is outputted from the nozzle until thegas pressure reaches the predetermined gas pressure is a first range; arange of the gas pressure inside the first gas passage from when the gaspressure reaches the predetermined gas pressure until the output of theliquid target material from the nozzle is stopped is a second range; andthe gas pressure inside the first gas passage within the first range ishigher than the predetermined gas pressure, and the gas pressure insidethe first gas passage within the second range is lower than thepredetermined gas pressure.
 5. The extreme ultraviolet light sourceapparatus according to claim 4, wherein the first range is greater thanthe second range.